G. Bashein

A Randomized Study of Carbon Dioxide Management during Hypothermic Cardiopulmonary Bypass

Eighty-six patients undergoing coronary artery bypass graft (n = 63) or intracardiac (n = 23) surgery were randomly assigned with respect to the target value for PaCO2 during cardiopulmonary bypass. In 44 patients the target PaCO2 was 40 mmHg, measured at the standard electrode temperature of 37 degrees C, while in 42 patients the target PaCO2 was 40 mmHg, corrected to the patients rectal temperature (lowest value reached: mean 30.1, SD 1.9 degrees C). Other salient features of bypass management include use of bubble oxygenators without arterial filtration, flows of 1.8-2.4 l.min-1.m-2, mean hematocrit of 23%, and mean arterial blood pressure of approximately 70 mmHg, achieved by infusion of phenylephrine or sodium nitroprusside. Neuropsychologic function was assessed with series of tests administered on the day prior to surgery, just before discharge from the hospital (mean 8.0, SD 5.8 days postoperatively, n = 82), and again 7 months later (mean 220.7, SD 54.4 days postoperatively, n = 75). The scores at 8 days showed wide variability and generalized impairment unrelated to the PaCO2 group or to hypotension during cardiopulmonary bypass. At 7 months no significant difference was observed in neuropsychologic performance between the PaCO2 groups. Regarding cardiac outcome, there were no significant differences between groups in the appearance of new Q-waves on the electrocardiogram, the postoperative creatine kinase-MB fraction, the need for inotropic or intraaortic balloon pump support, or the length of postoperative ventilation or intensive care unit stay. These findings support the hypothesis that CO2 management during cardiopulmonary bypass at moderate hypothermia has no clinically significant effect on either neurobehavioral or cardiac outcome.

Measurement of stroke volume with three-dimensional transesophageal ultrasonic scanning: comparison with thermodilution measurement.

The accuracy of measuring cardiac stroke volume with a new transesophageal phased array ultrasonic probe was investigated in 10 dogs. The method involved scanning the heart to obtain serial images covering the entire left ventricular cavity at end-expiration. An off-line computer analysis of the images was used to form three-dimensional reconstructions of the left ventricular cavity at end-diastole and end-systole, from which stroke volume was determined. Comparison with stroke volume determined by thermodilution during a wide range of hemodynamic conditions gave the following results for least-squares regression on 57 determinations (with the 95% confidence limits in parentheses): slope 0.95 (0.842-1.06), ordinate intercept 2.1 (2.0-2.2) ml, standard error of the estimate 4.1 ml, and correlation coefficient of 0.92 (0.87-0.95). Histologic examination of sections of esophagus surrounding the tip of the probe in nine dogs demonstrated minimal trauma to the esophageal wall, with eight specimens described as normal and one showing mild inflammation. The authors conclude that three-dimensional reconstruction of the left ventricular cavity from multiple transesophageal images offers a safe and accurate, although presently tedious, method for determining stroke volume.

An endoscopic micromanipulator for multiplanar transesophageal imaging

We have developed an esophageal probe with a precision micromanipulator and a transversely oriented 32 element ultrasonic array which operates at 3.5 MHz. The probe allows us to obtain multiple two-dimensional images of the heart with known angular relationships between them over a series of cardiac cycles. Our ultimate purpose is to acquire images for left ventricular volume estimation with a three-dimensional reconstruction method. Technical details of the probe design are given. In vitro tests have shown that the imaging plane can be angulated within 1.5 degree root mean square error. In vivo results with dogs have demonstrated its ability to obtain multiplanar short axis images of the heart.

A miniature position and orientation locator for three dimensional echocardiography

The accuracy of a new miniature prototype (6 mm/spl times/6 mm/spl times/9 mm) six dimensional (6D) locator sensor for three dimensional (3D) echocardiography was investigated. This new sensor identifies its 3D position and 3D orientation in space with respect to the position of a magnetic field generator. The sensor when attached to an ultrasound imaging transducer allows identifying and tracking the position and orientation in space of the ultrasonic imaging plane. The accuracy of this new miniature sensor was tested by rotating it on a lever arm apparatus which maintained a constant distance (R) from the sensor to the fixed point of rotation. At each rotational spatial position the sensors readings were used to calculate the fixed points position in space. The mean (MRE) and standard deviation (STDRE) of the radial error in this determination were calculated for N trials. The results with the apparatus: for R=10.6 cm were MRE=1.3 mm, STDRE=0.06 mm, N=500; and for R=18 cm they were MRE=1.8 mm, STDR=0.7 mm, N=500. It was then tested with a transcutaneous 5 MHz echo probe on 3D imaging a fixed position string target. The results in locating the position of the target was MRE=2.2 mm and STDRE=1.5 mm for N=45.<<ETX>>

Methodology for three-dimensional reconstruction of the left ventricle from transesophageal echocardiograms☆

A technique is presented for three-dimensional (3-D) reconstruction of the left-ventricular endocardial surface from multiplanar transesophageal echocardiograms, using both commercial software and investigator written Fortran programs for Intel 80286 and 80386 microcomputers. The approach provides quantitative global and regional cardiac performance measures and allows viewing the endocardial surface, at end-diastole and end-systole, from chosen perspectives. Anatomical landmarks are incorporated to aid in orientation. For regional calculation, the surface is divided into equal angular elements with each conceptually connected to the left-ventricular end-diastole centroid, forming a pyramidal volume element. This angular division automatically normalizes for heart size. The fractional change of these elements over the cardiac cycle provides a regional ejection fraction measure which is color-coded on the reconstructed endocardial surface. Composite perspective views, regional ejection fraction histograms and calculations of global end-diastolic, end-systolic, and stroke volumes, are all performed by the method.

Applying the CenterSurface model to 3-D reconstructions of the left ventricle for regional function analysis

Reconstruction of heart chambers from tomographic images has traditionally been done from either parallel or fixed position rotational scans. We introduce a method of reconstruction from random slice orientations, using labeled landmark features to guide fitting to a labeled predesigned surface-generating mesh. This method is applied specifically to ultrasound sector scanning, but is applicable to any tomographic imaging technique. Given surface descriptions of the left ventricle (LV) endocardium and epicardium at end diastole (ED) and end systole (ES) (or other time points), LV wall motion can be computed by matching the ED and ES surface features. Wall thickness at ED and ES is computed using the CenterSurface method. A new method of computing the CenterSurface is described.

Three-dimensional transesophageal echocardiography for depiction of regional left-ventricular performance: initial results and future directions

To assess the potential of a prototype transesophageal echocardiography probe for evaluating left-ventricular wall motion in three dimensions, we acquired images under anesthesia in 15 patients who had akinesia or dyskinesia and 8 patients who had normal function demonstrated on preoperative ventriculography. Shortaxis, oblique transgastric scans were obtained in 16 of the patients and four-chamber, long-axis oblique scans were obtained in 12 patients, with five patients (22%) yielding good-quality scans of both types. Off-line, we outlined the endocardial borders manually and used the outlines to make computer-generated three-dimensional models of the endocardial surfaces, color-tiled according to regional ejection fraction.Compared with contrast ventriculograms, the regional ejection fraction histograms derived from these models showed 86% concordance for detecting dyssynergy. However, the concordance between the ventriculograms and the color-tiled models in localizing the dyssynergy was only 67% overall. Uncertainty in rotational alignment between the reconstructions and the ventriculograms appeared to contribute to misreading the location of dyssynergy. In addition, the apical region appeared to have been missed in 8 (50%) of the shortaxis scans, whereas it was visualized in all long-axis scans.We conclude that three-dimensional analysis of the location, extent, and degree of left-ventricular dyssynergy is feasible from transesophageal echocardiograms and could have wide application in the study of regional ventricular function. However, improvements are necessary to enable the transducer to scan the cardiac apex more reliably from the short-axis viewpoint and to have a means for spatially orienting the images with respect to an external frame of reference.

Tools for Assessing Central Nervous System Injury in the Cardiac Surgery Patient

Despite improvements in surgical, anesthetic, and perfusion techniques in recent years, central nervous system (CNS) complications remain “a principal cause of the morbidity after open-heart surgery” [1]. Just as the improvement in cardiac outcome owes much to the growth in the number and sophistication of the tools to measure cardiac function, having better tools to assess brain function will contribute to development of new ways of avoiding CNS damage due to cardiopulmonary bypass (CPB). The importance to the CNS of oxygenator design, perfusion flow, pressure, arterial filtering, carbon dioxide tension, pharmacologic protection, and other factors can only be evaluated if proper measuring tools are available to the investigators.

Three dimensional echocardiography system for quantitative analysis of the left ventricle

The authors have previously reported two components of a methodology for acquiring and quantitatively analyzing three dimensional (3D) echocardiograms of the human heart. This report describes tools that they have developed to facilitate analysis of the left ventricle (LV), and to expand the applications of the technology to analysis of the right ventricle and mitral apparatus. Specifically the authors describe methods for 3D imaging, image analysis, surface reconstruction, and quantitative analysis of cardiac parameters. They also describe methods for facilitating these analyses and for adapting them to different clinical and research applications, such as measuring the relationship between different structures of the heart in 3D. The authors present clinical data to illustrate the applications of these technical innovations.

Left ventricular ejection fraction: single-plane and multiplanar transesophageal echocardiography versus equilibrium gated-pool scintigraphy☆

The relative accuracy and precision of estimating left ventricular ejection fraction (EF) in dogs were assessed by two-dimensional transesophageal echocardiography (2D-TEE) and by three-dimensional transesophageal echocardiographic (3D-TEE) imaging and reconstruction. This assessment was accomplished by comparing each echocardiographic method to a gated equilibrium blood pool radionuclide (RN) standard. By using both correlation and regression analysis, 2D-TEE performed reasonably well in estimating RNEF (correlation coefficient [r] = 0.80, slope = 1.01, intercept = 6.37, standard error of the estimate [SEE], 8.98), but not as well as 3D-TEE (r = 0.86, slope = 0.83, intercept = 3.38, SEE, 5.74). Using Altman and Blands methods of comparison analysis, it was found that 2D-TEE overestimated RNEF by 7% (standard deviation [SD], 8.8). This degree of overestimation was not consistent across the range of measurement. In contrast, 3D-TEE slightly underestimated RNEF by less than 3% and showed less variability (SD, 6.0). The accuracy of the 3D-TEE determinations was not dependent on the magnitude of EF. Additionally, a significantly higher proportion of the 2D-TEE measurements (0.30) compared with the 3D-TEE measurements (0.10) differed from RN values by more than 10% (P = 0.009, McNemars test). At the clinically important low end of the EF range (RNEF less than or equal to 35%), 2D-TEE may be expected (with 95% confidence) to be within -15% to +28% EF of reference values, whereas 3D-TEE can be expected to be within -8% to +5% EF relative to RN.(ABSTRACT TRUNCATED AT 250 WORDS)